JP2643229B2 - Communication method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a communication system in which a plurality of stations share one communication line using a time division multiplex system.

[Conventional technology]

In the conventional time division multiple access (TDMA) system, a unique time slot is allocated to all stations sharing a communication line (channel), and each station transmits data to a corresponding time slot. allocation
TDMA system and random access TD that uniquely determines the time slot in which the transmitting station should transmit data
There is MA method.

[Problems to be solved by the invention]

In the above-mentioned conventional fixed allocation TDMA system, a unique time slot is allocated to all stations, so that each station can reliably transmit data at fixed intervals. However, since it is necessary to wait until an assigned time slot arrives, a high throughput can be obtained at the time of high traffic, but an empty time slot increases at the time of low traffic, so that transmission efficiency deteriorates. On the other hand, in the random access TDMA system, since each station independently selects a transmission timing and transmits data, there is no need to wait as in the fixed allocation TDMA system,
This is advantageous during low traffic because it collides with data from other stations on the channel, and the data does not reach the target station, which risks the waste of the channel. .

[Means for solving the problem]

The system of the present invention is a communication system for performing communication between a plurality of communication stations to which a plurality of time slots on one communication line are individually assigned, wherein each of the plurality of communication stations has a range to be searched. Search range value storing means for storing a search range value indicated by the search time range; a first time slot on the communication line at the present time; and a second time slot arriving after the first time slot by the search range value. Determining means for examining whether or not a time slot assigned to the own station arrives in response to the occurrence of data in the own station; andin the determining means, the arrival of the time slot assigned to the own station is determined. When detected, the data is transmitted on the communication line in this time slot, but the arrival of the time slot assigned to the own station is not detected. Sometimes data transmission means for transmitting the data onto the communication line without waiting for the arrival of a time slot of the own station, and monitoring the state of traffic on the communication line and storing the data in the storage means based on the state of the traffic. Updating means for updating the searched range value.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings.
FIG. 2 shows a configuration example of a satellite communication network among various communication networks to which the present invention can be applied. In this network, a plurality of ground stations 1 communicate via one satellite station 2, each station 1 constantly monitors signals from the satellite station 2, and the ground stations communicate with each other without passing through the satellite station 2. Cannot communicate.

Referring to FIG. 1, one embodiment of the present invention, a station, comprises a TDMA control unit 10 having a transmission unit 11 and a reception unit 12,
A random transmission unit 13, a fixed allocation waiting unit 14, a table search unit 15, a transmission buffer unit 16, a retransmission control unit 17
, A traffic monitoring unit 18, a reception buffer unit 19,
And an antenna unit 20.

When data occurs in the station, the data is stored in the transmission buffer unit 16, and the length of the data is detected.
At this time, if the data length exceeds the length that can be accommodated in one time slot, this data is sent to the retransmission control unit 17.
To the table search unit.
To determine whether to perform random transmission or fixed allocation transmission.

FIG. 3 shows an assignment table 151 included in the search unit 15,
The pointer storage unit 152 storing the number of the current time slot and the search width storage unit 153 storing the number of slots to be searched are shown. Here, one frame is divided into 13 time slots from the first to the thirteenth,
It is assumed that the first to thirteenth time slots are allocated to thirteen stations A to M, respectively, and such frames are continuous. The table 151 defines such an assignment relationship between the time slot number and each station. Given the transmission data, the table search unit 15 knows the current time slot number from the storage unit 152 and the number of slots to be searched from the storage unit 153, respectively.
It is checked whether or not the slot number of the own station is within the search range. For example, if the contents of storage sections 152 and 153 are 6 and 4, respectively, the search range is slot number 6
To 10 If there is a slot number assigned to the own station within the search range, it is determined that the transmission data should be fixedly allocated and transmitted. If not, it is determined that the transmission data should be transmitted randomly. The number of slots to be searched stored in storage section 153 is updated based on the control parameters from monitoring section 18.

That is, the traffic monitoring unit 18 receives all reception signals received by the antenna unit 20 via the reception unit 12,
The traffic condition on the channel is checked based on these received signals, and control parameters are generated. This parameter is, for example, the number of collision slots (slots in which data of any station collides with data of another station on the channel) during the target period, and the number of used slots (data of other stations Divided by the number of slots used without collision). Search unit 15 based on these parameters
Increases or decreases the number of slots in the storage unit 153. This adjustment is
For example, it is performed as a guide so that the value of the parameter does not become 1 or more. That is, when the value of the parameter becomes 1 or more, the number of slots in the storage unit 153 is increased so that the collision is reduced. Further, if the way in which the number of slots to be searched is changed is made different for each station, each station can be given a priority order for channel access. When the number of slots to be searched is set to 0, random transmission is always performed. When the number of slots to be searched is selected to be equal to the total number of slots included in one frame length, fixed allocation transmission is always performed.

Next, an example of access according to the method of the present invention will be described with reference to FIG. On the satellite channel, 13 individually allocated to the 13 ground stations A to M sharing this channel
A plurality of frames composed of time slots are continuous. It is assumed that each station has a table having the same contents as the table 151 in FIG. In FIG. 4, the ground station F when the propagation delay from the ground station to the satellite station is about 2 time slots
An access example is shown. It is assumed that the number of slots to be searched stored in the storage unit 153 in the search unit 15 is four. In the station F, the data is originated at time t _1. At this time, the contents of the storage unit 152 of the station F is 7, it indicates that the time slot g at the present time i.e. the time t ₁ is the seventh time slot. Therefore,
The search range of the table 151 is from slot number to. When the slot numbers 7 to 11 are assigned to the stations G to K and the table 151 finds out that the slots 151 do not include the slot numbers assigned to the own station F, the search unit 15 sends the data to the random transmission unit 13. And the transmitting unit 13 transmits this data from the antenna unit 20 to the channel in the next time slot h. Next, the data has occurred at a time t _2. At this time, the contents of the storage unit 152 of the station F is 3, the time slot c is a third presently i.e. time t ₃
This indicates that this is the th time slot. Therefore, the search range of table 151 is from slot number to
It is. Since the slot number assigned to the own station F is included in the search range, the search unit 15 sends the data to the fixed assignment waiting unit 14, and the assignment waiting unit 14 waits until the sixth time slot f, and Send data to f.

Next, a case where data collision occurs on a channel will be described with reference to FIG. At station F, time t
_{3 When} data occurs at (time slot c), the table 151 in the station F is examined, and it is found that the slot f assigned to the own station F is included in the search range. Send on channel. On the other hand, in the station B, data occurs at the time t ₄ (time slot e), the table 151 in the station B is examined, and the time slot b of the slot number assigned to the own station B is included in the search range. The data is transmitted on the channel in the time slot f next to the current time slot e. As a result, stations B and F
Collide in the time slot f, and this collision is detected by the satellite station, and this fact is notified to the stations B and F from the satellite station. The monitoring units 18 of the stations B and F that have received this notification instruct the transmission waiting unit 14 to transmit the same data as the collision data stored in the retransmission control unit 17 described above. As described above, the data sent to the assignment waiting unit 14 is transmitted to the channel after waiting for the time slot of the own station. In this way, collisions are prevented from occurring again at least between the same stations. Thereafter, these stations transmit data on the channel by fixed allocation transmission until all the data in the transmission buffer unit 16 is exhausted.

〔The invention's effect〕

As described above, according to the present invention, by changing the search range according to the traffic state, it is possible to flexibly cope with the low traffic state to the high traffic state,
There is an effect that communication utilizing the advantages of the MA system and the random access TDMA system can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a diagram showing one configuration example of a network to which the present invention can be applied, and FIG.
4 is a diagram showing details of a table in the search unit 15, and FIGS. 4 and 5 are diagrams for explaining the operation of the present embodiment. 1 ... ground station, 2 ... satellite station, 10 ... TDMA control unit, 11 ...
... Sending unit, 12 ... Receiving unit, 13 ... Random sending unit, 14 ...
... fixed allocation waiting section, 15 ... table search section, 16 ...
... Transmission buffer unit, 17 retransmission control unit, 18 traffic monitoring unit, 19 reception buffer unit, 20 antenna unit, 151 table, 152, 153 storage unit.

Claims (1)

(57) [Claims] 1. A communication system for performing communication between a plurality of communication stations to which a plurality of time slots on one communication line are individually assigned, wherein each of the plurality of communication stations indicates a range to be searched. Search range value storage means for storing a search range value; a first time slot on the communication line at the present time; and a second time slot arriving after the first time slot by the search range value. Determining means for checking whether or not a time slot assigned to the own station arrives in response to the occurrence of data in the own station, and detecting the arrival of the time slot assigned to the own station in the determining means. Is transmitted on the communication line in this time slot when the time slot assigned to the own station is not detected. Data transmission means for transmitting the data onto the communication line without waiting for the arrival of a time slot of the own station; monitoring the state of traffic on the communication line; storing the data in the storage means based on the state of the traffic. And updating means for updating the searched search range value.